System Internationale unit

According to the modern convention, measurable quantities are expressed in SI (System Internationale) units and replace the centimetre-gram-second (cgs) system. In this system, the unit of length is a metre (m, the unit of mass is kilogram (kg) and the unit of time is second (s). All the other units are derived from these fundamental units. The unit of thermal energy, calorie, is replaced by joule (1 J = 107 erg) to rationalize the definition of thermal energy. Thus, Planck s constant... 

Energy is measured in maty different units around the world. In addition to the SI (Systeme Internationale) unit, the joule, energy can measured in calories, British thermal units (Btu), tormes of oil equivalent (toe), toimes of coal equivalent (tee), kilowatt-hours (kWh), and in physical units (e.g., cubic meters of gas, barrels of oil). The use of these physical units poses a problem, because the energy density of energy carriers can vary substantially between countries. For the other units, it suffices to fist the SI unit, if necessary, in combination with a local unit. 

Those who already have some familiarity with scientific units of measurement will know some of the SI (Systeme Internationale) units, and also know that some of the older c.g.s. (centimetre, gram, second) units are still widely used. For those needing them, it will be helpful to have some of these listed, with their conversion. 

This is one of the simplest of properties to define, understand and use. Density is mass per unit volume with SI (Systeme Internationale) units of kilograms per cubic meter. Specific gravity and relative density, the weight of the substance in relation to the weight of an equivalent volume of water, are often used synonymously. They are dimensionless but have the same numerical values as density. 

For historic reasons a number of different units of measurement have evolved to express quantity of the same thing. In the 1960s, many international scientific bodies recommended the standardisation of names and symbols and the adoption universally of a coherent set of units—the SI units (Systeme Internationale d Unites)— based on the definition of five basic units metre (m) kilogram (kg) second (s) ampere (A) mole (mol) and candela (cd). 

We also introduce the fundamental (base) units of the Systeme Internationale (SI), and discuss the way these units are employed in practice. 

While feet and yards are still used in Britain and other countries, the usual length is now the metre. At the time of the French Revolution in the 18th century and soon after, the French Academy of Sciences sought to systemize the measurement of all scientific quantities. This work led eventually to the concept of the Systeme Internationale, or SI for short. Within this system, all units and definitions are self-consistent. The SI unit of length is the metre. 

In a similar way, the Systeme Internationale has defined other common physicochemical variables. The SI unit of temperature T is the kelvin. We define the kelvin as 1/273.16th part of the thermodynamic temperature difference between absolute zero (see Section 1.4) and the triple point of water, i.e. the temperature at which liquid water is at equilibrium with solid water (ice) and gaseous water (steam) provided that the pressure is 610 Pa. 

Table 1.2 Several of the more common units that are not members of the Systeme Internationale...

The definition of mass in the Systeme Internationale scheme departs from the stated aim of formulating a rigorous, self-consistent set of standards. The SI unit of mass ... 

The System Internationale (SI) unit for radioactivity is becquerel (Bq), which is defined as one disintegration per second. The SI units and the conversion factors between curie and SI units are listed in Table 15.2. 

The units used to describe exposure and dose of ionizing radiation to living material are confusing, at best. First, the units have changed to an international system, SI, which stands for Systeme Internationale. We will use the SI system, but Table 12.2 compares the SI system with the older system. 

Under an international agreement concluded in 1960, scientists throughout the world now use the International System of Units for measurement, abbreviated SI for the French Systeme Internationale d Unites. Based on the metric system, which is used in all industrialized countries of the world except the United States, the SI system has seven fundamental units (Table 1.3). These seven fundamental units, along with others derived from them, suffice for all scientific measurements. We ll look at three of the most common units in this chapter—those for mass, length, and temperature—and will discuss others as the need arises in later chapters. 

Accurate measurement is crucial to scientific experimentation. The units used are those of the Systeme Internationale (SI units). There are seven fundamental SI units, together with other derived units Mass, the amount of matter an object contains, is measured in kilograms (kg) length is measured in meters (m) temperature is measured in kelvins (K) and volume is measured in cubic meters (m3). The more familiar metric liter (L) and milliliter (mL) are also still used for measuring volume, and the Celsius degree (°C) is still used for measuring temperature. Density is an intensive physical property that relates mass to volume. 

The most widely sanctioned set of units, the Systeme Internationale d Unites or SI set, is summarized here. In this book (as elsewhere, and for good reason ) this system has been only partially adopted. Thus, we use joules (instead of calories) but retain other earlier units, most importantly, Angstroms, atmospheres, and degrees Celsius. 

This derivation comes fi nm the book P/iysicoZ Chemistry of Surfaces by Adamson [2, p. 340] but uses Systeme Internationale des Unites... 

The Systeme Internationale d Unites, or SI for short, has gained widespread acceptance in the scientific and engineering community. Two of the base SI units—the ampere for electrical current and the candela for luminous intensity—will not concern us in this book. A third, the kelvin for temperature, will be discussed later. The others are the meter (m) for length, the kilogram (kg) for mass, and the second (s) for time. 

Since 1960, scientists worldwide have used a set of units called the Systeme Internationale d Unites or SI. The system is built on the seven base units listed in Tabie 1. The last two find little use in chemistry, but the first five provide the foundation of all chemical measurements. 

For centuries, units of measurement were fairly inexact. A person might mark off the boundaries of a property by walking and counting the number of steps. The passage of time could be estimated with a sundial or an hourglass filled with sand. Such estimates worked for ordinary tasks. Scientists, however, need to report data that can be reproduced by other scientists. They need standard units of measurement. In 1795, French scientists adopted a system of standard units called the metric system. In 1960, an international committee of scientists met to update the metric system. The revised system is called the Systeme Internationale d Unites, which is abbreviated SI. 

Recall from Chapter 2 that the universal unit system used hy scientists is called Le Systeme Internationale d Unit6s or SI. It is a metric system based on seven base units—meter, second, kilogram, kelvin, mole, ampere, and candela—from which all other units are derived. The size of a unit in a metric system is indicated by a prefix related to the difference between that unit and the base unit. For example, the base unit for length in the metric system is the meter. One tenth of a meter is a decimeter where the prefix deci- means one tenth. And, one thousand meters is a kilometer. The prefix kilo- means one thousand. 

For historical reasons, results of alkaline phosphatase estimations have been expressed in a variety of eponymic units. Some of these are listed in Table 2, which also gives generally accepted normal ranges (Dll, E3, G9, T8). Efforts are currently being made to standardize methods and to express results in units based on the Systeme Internationale (17). 

In System Internationale (SI) units, it is termed gray (Gy) and given by... 

The Systeme Internationale (SI) unit accepted worldwide for pressure is the Pascal, Pa ... 

For the most part the units, symbols, and terminology recommended by the International Union of Pure and Applied Chemistry and based on the Systeme Internationale (SI) have been used. A brief account of the SI is given in Appendix A (p. 556), Note that symbols for quantities are printed in italics, symbols for units in roman type. Non-SI units have been retained in a few cases—in particular calorie, atmosphere, and molarity—in view of the widespread use of them in chemical and biological work. 

The metric system has long been preferred for most scientific work. In 1960 an infernafional agreement set up a comprehensive system of units called the International System (le Systeme Internationale in French), or SI. The SI units are based on the metric system and units derived from the metric system. The most important fundamental SI units are listed in Table 5.1. Later in this chapter we will discuss how to manipulate some of these units. 

Systeme Internationale d Unites Donble-ended, linear arc tnbe. 

International System of Units (abbreviated SI from Systeme Internationale d Unites, die French version of the name). The conversion factors are reported only to four significant figures. 

For many years, scientists recorded measurements in metric units, which are related decimally, that is, by powers of 10. In 1960, however, the General Conference of Weights and Measures, the international authority on units, proposed a revised metric system called the International System of Units (abbreviated SI, from the French 5yst6me Internationale d Unites). Table 1.2 shows the seven SI base units. All other units of measurement can be derived from these base units. Like metric units, SI units are modified in decimal fashion by a series of prefixes, as shown in Table 1.3. We will use both metric and SI units in this book. 

The adoption of the international system of units, Systeme Internationale d Unites, or S.I. units for short, as the legal system in Great Britain and other countries is now complete, the system receiving official recognition at the Conference Generale des Poids et Mesures (C.G.P.M.) held in Paris attended by representatives from the National Physical Laboratory(N.P.L.) and the Bureau of Standards (U.SA.). Six basic units are involved metre (length), kilogramme (mass), second (time), ampere (electric current), kelvin (thermodynamic temperature) and candela (luminous intensity) from which other units are derived. 

---